The invention relates to a shaft cooler having a plurality of driven perforated comminuting rolls which are arranged horizontally adjacent each other beneath a layer of the material to be cooled, the rolls and the material layer disposed thereabove being cooled by a cooling air flow passing upwardly through the material layer.
For cooling calcined, burnt or sintered material, grid coolers of various types, drum coolers and tube coolers are known. However, in some cases they have a relatively poor efficiency and in some cases they are very expensive to construct.
For these reasons, attempts have been made recently to develop shaft cooler designs which combine the advantages of low plant cost, good cooling efficiency and uniform quality of the cooled product.
It has been found expedient to provide the shaft cooler with a plurality of driven comminuting rolls arranged horizontally adjacent each other to comminute large agglomerations of material after a certain pre-cooling but prior to an aftercooling, in order to prevent inadequately comminuted material lumps whose cores are still hot from being discharged from the cooler.
In a known shaft cooler of the aforementioned type (DT-OS 1,558,609) there is disposed above the comminuting rolls a relatively high material column (which in a practical construction of such a shaft cooler amounts to several meters). The cooling air is supplied through a space free of material beneath the comminuting rolls, cools the rolls and then passes upwardly through the column of material disposed thereabove. The shaft cross-section tapers upwardly in such a manner that at least the upper region of the material column is held by the increased air velocity in a state similar to a fluidized bed.
However, the effect aimed at with this shaft cooler turns out to be hardly attainable in practice because the cooling air rising in the cooling shaft (in particular at the necessary high pressure) tends to seek preferred flow passages. In any case, a reliable distribution and loosening, similar to that in a fluidized bed, of the material in the uppermost zone of the high material column, can only be obtained with a very great expenditure of energy.
A further disadvantage of this known shaft cooler is that the material lumps comminuted by the comminuting rolls disposed at the lower end of the high material column are not subjected to adequate aftercooling in the cooling shaft when they simply fall through the space free of material provided beneath the comminuting rolls, through which cooling air is passed, before they reach a discharge hopper. On the other hand, if for this reason a special aftercooling means (for example a grid cooler) must be provided, the desired advantage of less expenditure on plant is lost.